This invention relates to a bubble memory device and a method of manufacturing the same.
A prior art bubble memory device has a construction as shown in FIGS. 1 and 2. A ceramic or the like insulating substrate 1 has a central recess formed in the top surface, in which a bubble memory chip 2 is held in a fixed position. Outside the insulating substrate 1, X- and Y-direction driving coils 3a and 3b are wound in perpendicular X- and Y-directions to provide an in-plane rotating magnetic field to the chip 2. The insulating substrate 1, chip 2 and coils 3a and 3b are molded together as a molded assembly 4. The molded assembly 4 has central recesses 4a and 4b formed in the top and bottom surfaces in which are provided magnet blocks 7a and 7b. Each of the central recesses has a central deep portion of a depth D of about 0.4 mm, leaving corner shoulders on which the magnet block rests. The magnet blocks 7a and 7b respectively include plate-like permanent magnets 5a and 5b, which provide a bias field to the chip 2, and field homogenizer plates 6a and 6b for homogenizing the magnetic flux from the permanent magnets 5a and 5b`. The permanent magnets 5a and 5b are covered by a shield case 8 made of Permalloy.
In the bubble memory device as described above, the molded assembly 4 and magents blocks 7a and 7b are usually assembled together in a manner, which will now be described with reference to FIGS. 1 and 2. First, an adhesive is applied to the bottom surfaces of the central deep portions of the recesses 4a and 4b. The magnet blocks 7a and 7b are then set in the recesses to rest on the corner shoulders and bonded by the adhesive. This method of assembling, however, requires a great deal of time for such operations as applying the adhesive, setting the magnet blocks 7a and 7b for bonding and hardening the adhesive. Besides, it is necessary to form the magnet block accommodation recess 4a or 4b having the central deep portion of about 0.4 mm depth. The deep portion is necessary because the recess bottom tends to swell at the time of molding and in the absence of the deep portion, the magnet block would inevitably abut on a swollen area and become inclined to disturb parallelism of the two magnet blocks. Thus, the adhesive is applied to the deep portion and the magnet block resting on the shoulder is bonded to the mold assembly 4 by the adhesive. With this construction, however, moisture is liable to reach the interior coils via a gap between the magnetic block and the shoulder, adhesive and pin holes formed in the mold. Further, the deep portion of about 0.4 mm depth calls for the shoulder of a corresponding height and the device thickness is disadvantageously increased by 0.4.times.2=0.8 (mm). Further, it is general practice that the plenum between the deep portion bottom and the interior coil layer is made comparatively thick to suppress the generation of swelling, thus aggravating the increase in the device thickness.